<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>下拉菜单</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .ddd{

            width: 200px;
            margin: 0 auto;
        }
        .d{
            height: 40px;
            line-height: 40px;
            background-color: aqua;
            border: 1px solid hotpink;
        }

        .u{
            height: 0;
            background-color: olivedrab;
            list-style: none;
            overflow: hidden;
            transition: all ease 0.5s;
        }
        .dd:hover > .u{
            height: 90px;
        }
    </style>
</head>
<body>
<div class="ddd">
    <div class="dd">
        <div class="d">市内新闻</div>
        <ul class="u">
            <li>市内超市遭抢</li>
            <li>市内超市遭抢</li>
            <li>市内超市遭抢</li>
            <li>市内超市遭抢</li>
        </ul>
    </div>
    <div class="dd">
        <div class="d">省内新闻</div>
        <ul class="u">
            <li>省内超市遭抢</li>
            <li>省内超市遭抢</li>
            <li>省内超市遭抢</li>
            <li>省内超市遭抢</li>
        </ul>
    </div>
    <div class="dd">
        <div class="d">国内新闻</div>
        <ul class="u">
            <li>国内超市遭抢</li>
            <li>国内超市遭抢</li>
            <li>国内超市遭抢</li>
            <li>国内超市遭抢</li>
        </ul>
    </div>
    <div class="dd">
        <div class="d">国际新闻</div>
        <ul class="u">
            <li>国际超市遭抢</li>
            <li>国际超市遭抢</li>
            <li>国际超市遭抢</li>
            <li>国际超市遭抢</li>
        </ul>
    </div>
</div>

</body>
</html>